Ion implantation is a physical process that is employed in semiconductor apparatus fabrication to selectively implant dopant into a semiconductor workpiece and/or wafer material. Thus, the act of implanting does not rely on a chemical interaction between a dopant and the semiconductor material. For ion implantation, dopant atoms/molecules are ionized and isolated, sometimes accelerated or decelerated, formed into a beam, and swept across a workpiece or wafer. The dopant ions physically bombard the workpiece, enter the surface and typically come to rest below the workpiece surface in the crystalline lattice structure thereof.
In ion implantation, energy contamination (EC) is the fraction of the total dose delivered to a wafer at an undesired energy, thereby causing a deeper or shallower implantation than desired. For example, in ion implanters that decelerate the ion beam prior to reaching a workpiece, EC can be a major problem because it can result in poor device performance. EC can result from various processes within the ion implantation system (such as within an accelerator or decelerator located along a beam path) that may act to cause ions to change their initial charge value (e.g., a charge exchange reaction). When a high speed ion comes in close proximity to another molecule or atom of a gas, the ion may pick up an electron from the molecule or atom (i.e., an electron “picking up” reaction), or may lose an electron to the molecule or atom (i.e., a charge stripping reaction). The former reaction reduces the value of ion charge by one; for example, a singly charged ion can become a neutral, that is, an electrically neutral atom. The latter increases the value of ion charge by one (e.g., a singly charged ion becomes a doubly charged ion). Because most EC arises from charge-exchange in the ion beam, the traditional method of reducing energy contamination focuses on minimizing charge exchange reactions.
However, only focusing on minimizing charge exchange can neglect other sources of EC. Accordingly, suitable systems and methods for providing more sensitive implants while further minimizing EC are desired.